One form of pipeline includes, at least during construction of the pipeline, an inner component at least partially enclosed by a formable outer component. At least during construction, the inner component typically includes a plurality of inner component sections in end-to-end relationship. Each of the inner component sections may be, for example, a pipe section, a core unit or an inner form. If a pipe section or core section is used, such section remains as a permanent part of the pipe. However, if a form is used, it is removed after the outer component is applied, and in this event, the form is part of the pipeline only during construction of the pipeline.
The formable outer component may be a variety of flowable material used to encase, or partially encase, the inner component. For example, the formable outer component may be a cementitious material, such as concrete or other materials, which is flowable and curable to form a casing, or partial casing, for the inner component. Alternatively, the formable outer component may be a cushion or a noncurable material, such as sand or soil. The resulting pipeline can be made capable of carrying various materials, including liquids.
My prior U.S. Pat. Nos. 3,830,606 and 4,087,219 disclose apparatuses for forming underground pipelines of the type described above. Each of these patent constructions includes a receptacle for receiving an inner component section and a bulkhead at one end of the receptacle. The bulkhead has an outlet opening so that the inner component section can be passed through the outlet opening and be joined to a previously laid inner component section. The formable outer component is flowed around an inner component section as the inner component section is moved through the outlet opening of the bulkhead.
Both of these apparatuses function very satisfactorily as do the methods disclosed in both of my prior patents. However, the methods described in my prior U.S. patents are not as well suited as desired for certain applications.
More particularly, the placement or flowing of the outer component simultaneously with the passing of the inner component section through the outlet opening of the bulkhead can present problems. For example, if the flowable outer component is not available, the placement of the inner component sections must be abated, and this can delay completion of the job and increase job costs. Also, there are instances in which placement of the inner component sections can proceed at a fastener rate than the placement of the outer component sections. In addition, there is a potential problem of leakage of the flowable outer component through the outlet opening in the bulkhead. Also, when the inner component section has an axially protruding bell for attachment to an adjacent inner component section, the pipe-laying apparatus must have special features to accommodate the bell and to avoid leakage of the outer component through the outlet opening of the bulkhead. Finally, a sufficient amount of the outer component must be used to float and, therefore, support the inner component sections, otherwise the lower regions of the inner component section would not be encased in the outer component.